It is well known to use a retractable antenna on portable radio equipment. Commonly the retractable antenna is rendered inoperative in the retracted position. Sometimes it is arranged that a second, eg internal, antenna may be rendered operative in place of the retractable antenna when the latter is retracted. Such an antenna configuration is disclosed in British patent application GB-A-2,219,911.
In the context of portable telephones it is desirable to make the retractable antenna as small as possible. In European patent application EP-A-0,467,822 there is disclosed a slim, flexible, retractable rod antenna having for example, a stiff coiled configuration enclosed within a dielectric sleeve. In this case a second antenna in the form of an antenna coil is carried by the outer end of the antenna rod. When the rod antenna is in the retracted position it is disconnected from the radio circuitry in favour of the coil antenna.
U.S. Pat. No. 4,868,576 discloses an antenna for a portable telephone, including a slim, retractable radiating element comprising a coil of silver plated beryllium copper wire. The coil is moulded inside a flexible plastic sleeve having an external diameter of only 100 mils (2.54 mm). In this case the retractable antenna is mounted to extend through a helical winding coupled to the radio circuitry. In the extended position the retractable element is capacitively coupled to the helical winding, but in the retracted position it is substantially decoupled therefrom.
A drawback with the slim retractable antennas disclosed in EP-A-0,467,822 and U.S. Pat. No. 4,868,576 is that, due to their flexibility, there is a tendency for them to move and rattle within the radio housing, particularly when in the retracted position. It will be noted that in these prior art examples the antenna is supported only in the region of the aperture in the housing through which the antenna extends. It will be appreciated therefore, that when the antenna is retracted, there is a substantial portion of the retractable antenna element which is present, but unsupported, within the radio housing. Because of the flexible nature of the retractable element the free end thereof within the radio housing is liable to move and rattle against the housing walls particularly when the radio is being carried or otherwise moved.